How sharp is the K 50 f/1.2? How much does it sacrifice for its speed? Is it just a status symbol? These questions have come up a few times, so today I thought I would take some shots around the house to address them, at least to my satisfaction.

These are not scientific tests, whatever those might be. I have shot with this lens for a while, so I have a certain feeling for it. But I have never dedicated a session to investigating that feeling closely. Look at this test as more of a photographer's view, and not a firm and absolute metric.

I shot inside to avoid flooding the lens with light on this lovely spring day. I chose close and medium distance subjects. I gave myself a cap of a couple hours to get everything done.

After this introduction I will present the shots in three groups, with my comments. Everything was shot hand-held with SR on, since that is how I use my camera most of the time. And that is the benefit of a fast lens. I used an after-market metal lens hood. Perhaps I could have a better one, but this is better than nothing.

Perhaps unfortunately I had a filter on the lens. Normally I never use these, but the front element here is quite exposed when the hood is off. I have got in the habit of using a filter just to protect the lens when it is moving around. I forgot to take it off. But under these conditions (no strong light, not shooting into the light, etc.) I do not think it would have made any significant difference. if you wish, consider that the lens will do better than what this test shows, without such a filter.

Here are the first couple of images. They have been cropped slightly but otherwise represent what was in the viewfinder. In terms of processing I shot RAW and converted with Adobe Camera RAW (ACR). I use the Auto button and then compensate to optimise the curve, as sometimes Auto screws things up. Every image I will produce in this thread was processed identically at least that far.

Secondly, I have a standard Photoshop workflow in my old beaten up version, which uses a slight initial sharpening algorithm plus curve correction. Before producing a web image I reduce the size and then sharpen again, this time more noticeably. The images I will label "processed" have these extra steps. The ones I label "unprocessed" have the resizing (obviously) but nothing else.

Nut bowl at f/1.2 (processed)

Nut bowl at f/2 (processed)

Yes, I know they are not identically composed. I shot a bunch of frames at both apertures and chose the best one. Remember I am doing this hand-held.

I decided I needed a bit more control, so I targeted a calendar we have up in the kitchen. Yes, it's the old M.C. Escher -- I still love his work!

These are both wide open at f/1.2 from medium distance. They have been cropped slightly (and made square).

I should mention here that the camera is the K20D in Manual mode. I meter using the green button and then compensate as needed. I find I always need to give it one stop more light from that point. I used the "catch in focus" technique, but it is still true that the range at which the camera thinks the subject is in focus is much larger than reality. So I take several shots, slowly turning the focus ring...very slowly! Here's a tip: The sharpest shots will be the ones at the closest end of the "in focus" range.

Escher print at f/1.2 (unprocessed)

Escher print at f/1.2 (processed)

The processed image has additionally been converted to mono. This cleans up the purple fringing that is evident even at this size. For example, look at the lizard climbing onto the book. Ignoring the fact that the image is tinted blue in the first place, his back is noticeably purple from the fringing. (Testing with a woodcut simulates resolution tests!)

The sharpening has really helped as well. I would have no problem using this image, despite the fact it is at f/1.2.

Here is a similar shot at f/2. Again I present the unprocessed shot followed by one where I converted to mono and applied some sharpening.

I'd like to say here that every shot you make in RAW can benefit from judicious sharpening. You will find that a lot of pros sharpen once out of the camera and a second time to target their distribution medium, whether that be print or screen. Basically, that is what I do.

Escher print at f/2 (unprocessed)

Escher print at f/2 (processed)

The exposure on these images worked out to be different. You can see that clearly from the bottom of the panels. The processed photo is a lot whiter than the grey in the unprocessed photo.

Again, I much prefer the processed version. I am sure with more care, better results would be achieved, but I was trying to be consistent here for the purposes of comparison.

Robin, I'm not sure what's up but I don't get so much purple at f1.2...
would say it's slightly OOF.
I am actually very surprised by the sharpness of this lens at f1.2...
it's not as good as my K55/1.8 until f2.8 but it's still VERY usable IMHO

Here I will cover a few issues I expect commentators to address, and I will then wrap up with my conclusions.

Colour
I realise that these test don't say anything about the colour rendering of this lens. But that is something I have never had any problems with. It renders like a Pentax should!

Crops
I am not presenting 100% crops as they basically don't matter. Only what you see here on the screen or in print matters. And I have made perfectly decent prints from images that look rather poor at 100%. The screen is already quite punishing compared to many prints. Of course if you need to print A1 or A0 size at full resolution, you will see more detail and more problems -- especially if that is all you are looking for. This depends on the distance you are from the print when viewing, lighting, paper, ink and other factors.

In short, this is a real world test. In the real world I present most of my photos as you see them here.

Smaller Apertures
I did not bother testing smaller apertures because I know from experience that this lens performs well at f/4 and so on. No-one pays the money for an extremely fast lens to use it specifically at a middling aperture. It is when the lens is close to wide open that we need to investigate performance.

Wide Open
This lens is usable at f/1.2. The biggest problem is getting focus, due to the extremely narrow depth of field and the fact that the body indicates that correct focus is achieved over a much wider range than is desirable. If you are far enough away from your subject you will get more DOF. If you are very good at manually focusing you will be a happier person. Learn to take numerous shots while focus bracketing.

The purple fringing at f/1.2 can be severe. For a mono image this is simply irrelevant. For colour, it will depend on your subject. Here is a front-lit subject with high contrast and fine detail with lots of white. I have not corrected for any fringing. Do you see a problem?

Schweppes at f/1.2 (processed)

Bottom Line
Though you may have to take more care at f/1.2, stopped down to f/2 or more, this lens rocks. Of course there are other lenses that fast, but they in turn generally need to be stopped down one or two to get an optimal image.

Is the fastest of fast fifties worth the extra money? Only you can decide. But I hope this has given you some useful data points.

Robin, I'm not sure what's up but I don't get so much purple at f1.2... would say it's slightly OOF.

That could be, but I'm not likely to get it any more in focus. I do think it is down to the subject. Being a print of a woodcut, this has highly contrasting lines placed closely together. It is probably a worst-case scenario. Some subjects show this aberration more than others. See the cat photo where it is just not a problem!

. . .Bottom Line
Though you may have to take more care at f/1.2, stopped down to f/2 or more, this lens rocks. Of course there are other lenses that fast, but they in turn generally need to be stopped down one or two to get an optimal image.

Is the fastest of fast fifties worth the extra money? Only you can decide. But I hope this has given you some useful data points.

I agree that this lens rocks as does its brother the A f1.2. Both are easy to mf with an aftermarket screen as well.

I have both K50/1.2 and K55/1.8.
Haven't pitched them against each other side by side in proper test.
From real life shots I do think until f2.4-2.8 the 55 is tad sharper but even despite it's extra 5mm the 50 just blows it off the water if it comes to OOF rendering.
Anyway, to the purple stuff and sharpness wide open.
Just two shots (OK, one and it's 100% crop):
full frame from K10D f1.2 ISO200 1/125s:

Nice. Thanks for the extra info and taking the time to post some shots. There certainly is no problem there at f/1.2!

I think that there might be some serious sample variation from all the reviews I have read of the fast Pentax 50s. Some say that the A model is distinctly better while others say they are identical. Some complain about "this" while others say "that". I can only deal with the lens I have, which is good enough for me!

But day to day I reach for the FA 43mm Limited instead. It's a lot lighter and more compact, renders well at f/2 and has a look I prefer.

On the other hand, every time I use the K lens I am rewarded.

P.S. I started this thread (partially) for people who wanted to compare the fast Nikkor 50 to the Pentax. I can't do that, but hope what I have here helps.

I have 43 too.
and I've found myself heading in oposite direction compared to you Robin.
I actually reach for 31 + 50/1.2 more often than for 43. Though if I'm taking one lens only it's 43 most of the time.
I think at f2 it's sharper that K50 but I prefer bokeh on 50.

glad to see people enjoying their 1.2s'. anyway I think the K55 and 1.2's are pretty close to judge. there are instances at wide open and other apertures at the same openings that the other seems to be very very slightly sharp than the other. but from what I could certainly tell, these lenses have extremely benefitted from RAW processing, including the 50/f2.

I'll contribute with another real world example, plus a crop for the pixel-peepers. This lens is, as someone else already said, surprisingly sharp wide open. And it gets better stopped down. I hope to do a re-run this summer of my 50's shootout from last summer. With some additions (and fixing the slight fumble of not having the 1.2 in focus...), this would include K50/1.2 K50/1.4 K55/1.8 and M50/1.7 maybe a kit zoom for reference and whatever else I have at hand when it comes down to doing the shots.

Hope nobody saw the photo I had here originally. A little mix-up occurred and the pic was actually taken with the K50/1.4 and not the 1.2. Here is one from the 1.2 though.